There are in existence a number of prior art devices for removing surface dirt from a factory conveyor belt. One type comprises a scraper element made of a block of rubber about a foot long and of a width conforming to the width of the conveyor belt, which is urged against the moving belt by a hinge and counter-weight arrangement. In another known type of conveyor scraper, the scraper blade is connected to an arm which is urged against the conveyor belt by a torque applying mechanism such as a spring steel arm or air cylinder. In another type of known device, the scraper blade is biased towards the conveyor belt by means of a coil spring. The wear elements of these conveyor scrapers are relatively short in length and tend to wear quickly. As a result, the wear element of these scrapers must be replaced on a relatively frequent basis, which entails high labour costs. Also, these prior art scraper designs are inefficient because a relatively high percentage of the total volumetric area of their scraper blades is unusable. In some cases, one inch of a five inch blade must be thrown away--this represents a 20 % waste of material. All of these prior art scrapers therefore suffer from the common disadvantage of entailing high maintenance (parts and labour) costs.
The scraping apparatus disclosed in the U.S. Pat. No. 2,545,882, which issued to Hall on 20 Mar., 1951, addresses the problem of frequent replacement of the wear element, by providing a relatively long scraper strip mounted about a roller. However, this apparatus uses a cumbersome mechanical arrangement for maintaining the scraper strip in contact with the belt under tension. This unwieldy mechanism would seem to make the Hall scraper unsuitable for mounting in most conveyor chutes which have a limited space to accomodate a scraper unit. The Hall unit has not to the applicant's knowledge been exploited on a commercial basis.
The conveyor belt cleaning device disclosed in U.S. Pat. No. 4,290,520, which issued to Rhodes on 22 Sept., 1981, avoids the need for independent suspension springs or other mechanical adjustments of the mounting of the scraper blade, by utilising a pressurized air bag. However, the use of this design limits the length of the scraper blade, since the scraper unit must be compact in order to fit into the space provided in typical conveyor chutes. As a result, the Rhodes conveyor scraper also entails relatively high maintenance costs caused by relatively frequent service intervals as well as a high percentage of waste by volume of the wear element.